The present invention relates to methods of producing solute-rejecting dynamic membrane filters, and also to filters including such membranes.
Solute-rejecting dynamic membrane filters are well known, for example as described in U.S. Pat. No. 3,577,339 of May 4, 1971. Such known filters include a porous substrate (e.g., porous metal, ceramic, or carbon) having a relatively large pore size (e.g., 5 to 50 microns in diameter) on which has been deposited a bed of smaller particles (e.g. in the range of 0.01-100 microns in diameter) of an inert material, for example diatomaceous earth, perlite, asbestos fibres, cellulous fibres, dried silica gel, and carbon. The thin bed of particles functions as a finely pored body and remains uniformly distributed even when deposited in the presence of a cross-flow velocity parallel to the surface of the membrane. The thickness of the bed is a function of the cross-flow velocity, and therefore, it is often useful to deposit the bed under turbulent flow conditions. The filters are easily re-established by depositing a new bed of the particles on the porous substrate.
In order to make the known dynamic membrane filters solute-rejecting, it is generally necessary to include a solute-rejecting additive, for example, a neutral organic polymer, polyelectrolyte, organic or inorganic ion exchanger, or hydrous metal oxide, as described in column 3, lines 12-23 of the above-cited patent. Moreover, it is generally difficult, in the known procedures, to tailor the produced dynamic membrane to have a preselected molecular weight cut-off characteristic.